Skyline Owners Forum banner

1 - 20 of 25 Posts

·
Tyne/Wear/Tees Arse Rep/Gtr Shop Rep
Joined
·
11,412 Posts
Discussion Starter #1
What gives the RB series such a distinctive engine/exhaust note?

you can tell a Skyline a mile off, i have owned a few cars with straight six engines and none have ever sounded as good.
 

·
Registered
Joined
·
822 Posts
Me too!! And what a great sound it is.

Sound has something of a BMW 6-cilinder, but lower...

LOVE IT!! :)

But why it is making such a nice exhaust note, I really don't know.
 

·
Autobahn Burner
Joined
·
1,223 Posts
All RB engines except the RB 30 (86x86 so square) are overs quare, (bore is greater than stroke), rb25 is 86x71.7mm, rb26 is 86x 73.7mm All bmw straight 6's are under square (bore is less than stroke)
over square engines are generally rev happy due to lower piston speeds can generally rev higher so trade bottom end torque for hp higher in the rev band
the most extreme examples being F1 engines
Under square engines are tourque monsters the flame front acts on the piston for a greater amount of time. They generally cannot rev as high because the piston has to move more distance in the same time as a shorter stroke engine so they have more stress at the same speed, and at very high rpm the piston can actually out run the flame front.

Over square cars will have a deeper tone as due to the lower piston speeds, the hot gas from combustion will still be expanding a bit when the exhaust valve opens(most over square engines like the RB have more valve overlap built in to help at high engine speeds)
On an under square motor the gas will have almost completely finished expansion because the rapid expansion of the piston due to the longer travel, and since they generally do not rev as high as oversquare motors they will have less valve overlap. leading to a tone not quite as deep as our beloved RB's
 

·
Registered
Joined
·
1,637 Posts
Oversquare cars will have a deeper tone as due to the lower pision speeds, the hot gas from combution will still be expanding a bit when the exaust valve opens(most oversquare engines like the RB have more valve overlap built in to help at high engine speeds)
On an undersqaure motor the gas will have almost completely finihed expansion due to the rapid expansion of the pistion due to the longer travel, and since they generally do not rev as high as oversquare motors they will have less valve overlap. leading to a tone not quite as deep as our beloved RB's

That explains V8's and the like then.... always wondered why they didnt rev as high :)

Cheers
 

·
Censored
Joined
·
7,453 Posts
All RB engines except the RB 30 (86x86 so square) are oversquare, (bore is greater than stroke), rb25 is 86x71.7mm, rb26 is 86x 73.7mm All bmw straight 6's are undersquare (bore is less than stroke)
Pver square engines are generally rev happy due to lower pistion speeds can generally rev higher so trade bottom end tourqe for hp higher in the rev band
the most extreme examples being F1 engines
Undersqure engines are tourqe monsters the flame front acts on the pistion for a greater amount of time. They generally cannot rev as high becuase the pistion has to move more distance in the same time as a shorter stroke engine so they have more stress at the same speed, and at very high rpm the pistion can actually out run the flame front.

Oversquare cars will have a deeper tone as due to the lower pision speeds, the hot gas from combution will still be expanding a bit when the exaust valve opens(most oversquare engines like the RB have more valve overlap built in to help at high engine speeds)
On an undersqaure motor the gas will have almost completely finihed expansion due to the rapid expansion of the pistion due to the longer travel, and since they generally do not rev as high as oversquare motors they will have less valve overlap. leading to a tone not quite as deep as our beloved RB's
excellent informative post :)
 

·
Seasoned Member
Joined
·
4,929 Posts
:yum:
All RB engines except the RB 30 (86x86 so square) are oversquare, (bore is greater than stroke), rb25 is 86x71.7mm, rb26 is 86x 73.7mm All bmw straight 6's are undersquare (bore is less than stroke)
Pver square engines are generally rev happy due to lower pistion speeds can generally rev higher so trade bottom end tourqe for hp higher in the rev band
the most extreme examples being F1 engines
Undersqure engines are tourqe monsters the flame front acts on the pistion for a greater amount of time. They generally cannot rev as high becuase the pistion has to move more distance in the same time as a shorter stroke engine so they have more stress at the same speed, and at very high rpm the pistion can actually out run the flame front.

Oversquare cars will have a deeper tone as due to the lower pision speeds, the hot gas from combustion will still be expanding a bit when the exhaust valve opens(most oversquare engines like the RB have more valve overlap built in to help at high engine speeds)
On an undersqaure motor the gas will have almost completely finished expansion because the rapid expansion of the pistion due to the longer travel, and since they generally do not rev as high as oversquare motors they will have less valve overlap. leading to a tone not quite as deep as our beloved RB's
Thanks for that mate!! Very informative! :cheers: Just have to memorise that when someone asks me the same question !!
 

·
Tyne/Wear/Tees Arse Rep/Gtr Shop Rep
Joined
·
11,412 Posts
Discussion Starter #8
All RB engines except the RB 30 (86x86 so square) are oversquare, (bore is greater than stroke), rb25 is 86x71.7mm, rb26 is 86x 73.7mm All bmw straight 6's are undersquare (bore is less than stroke)
Pver square engines are generally rev happy due to lower pistion speeds can generally rev higher so trade bottom end tourqe for hp higher in the rev band
the most extreme examples being F1 engines
Undersqure engines are tourqe monsters the flame front acts on the pistion for a greater amount of time. They generally cannot rev as high becuase the pistion has to move more distance in the same time as a shorter stroke engine so they have more stress at the same speed, and at very high rpm the pistion can actually out run the flame front.

Oversquare cars will have a deeper tone as due to the lower pision speeds, the hot gas from combustion will still be expanding a bit when the exhaust valve opens(most oversquare engines like the RB have more valve overlap built in to help at high engine speeds)
On an undersqaure motor the gas will have almost completely finished expansion because the rapid expansion of the pistion due to the longer travel, and since they generally do not rev as high as oversquare motors they will have less valve overlap. leading to a tone not quite as deep as our beloved RB's

Now thats a bloody good answer
 

·
Autobahn Burner
Joined
·
1,223 Posts
piston speed=
stroke in mm* (rpm)*60/1,000,000=KMH
so on an rb25 at redline its 30.114kmh doesn't seem like that much eh?
then you think, that piston goes from 0kmh(TDC) to 30kmh then back to zero(BDC) back to 30 and back to zero in .00857seconds.
to put that in perspective, the piston endures 387g's of acceleration or deceleration 4 times per revolution!
a formula one motor at 18000 rpm, piston speed is only 43.2 kmh but about 900g's of acceleration or deceleration per piston movement!
 

·
Tyne/Wear/Tees Arse Rep/Gtr Shop Rep
Joined
·
11,412 Posts
Discussion Starter #15
loving this thread, has to be one of if not the most informitive for a long time
 

·
Forum loiterer!
Joined
·
1,707 Posts
piston speed=
stroke in mm* (rpm)*60/1,000,000=KMH
so on an rb25 at redline its 30.114kmh doesn't seem like that much eh?
then you think, that piston goes from 0kmh(TDC) to 30kmh then back to zero(BDC) back to 30 and back to zero in .00857seconds.
to put that in perspective, the piston endures 387g's of acceleration or deceleration 4 times per revolution!
a formula one motor at 18000 rpm, piston speed is only 43.2 kmh but about 900g's of acceleration or deceleration per piston movement!
:worshippy: :worshippy: :worshippy: :worshippy: :worshippy: :worshippy: :worshippy: :worshippy: :worshippy: :worshippy:
 

·
Registered
Joined
·
1,459 Posts
To help put in to perspective just how quickly the pistons are
moving in an engine, at 7500rpm they are going up and down
125 times a second! thats how quickly things happen inside
an engine.
 

·
confused.com
Joined
·
6,592 Posts
more more ...this the sorta stuff i would like to know...so i actually understand the "bang under the bonnet" .....and how to make it better
 

·
confused.com
Joined
·
6,592 Posts
ok so if im reading this right .....

All RB engines except the RB 30 (86x86 so square) are overs quare, (bore is greater than stroke), rb25 is 86x71.7mm, rb26 is 86x 73.7mm All bmw straight 6's are under square (bore is less than stroke)
over square engines are generally rev happy due to lower piston speeds can generally rev higher so trade bottom end torque for hp higher in the rev band
the most extreme examples being F1 engines
Under square engines are tourque monsters the flame front acts on the piston for a greater amount of time. They generally cannot rev as high because the piston has to move more distance in the same time as a shorter stroke engine so they have more stress at the same speed, and at very high rpm the piston can actually out run the flame front.

Over square cars will have a deeper tone as due to the lower piston speeds, the hot gas from combustion will still be expanding a bit when the exhaust valve opens(most over square engines like the RB have more valve overlap built in to help at high engine speeds)
On an under square motor the gas will have almost completely finished expansion because the rapid expansion of the piston due to the longer travel, and since they generally do not rev as high as oversquare motors they will have less valve overlap. leading to a tone not quite as deep as our beloved RB's
the rb30 is therefore made by increasing the stroke not the bore.....similarly the 26 over the 25. so what sort of capacity would an over bored block with 88mm pistons and 73.7mm stroke give ....

(in other words an rb26 stroke with a bore of 88mm........giveing a slightly longer flame time ala the longstroke undersquare with the relatively high rev capabilites of the over square?)

i get somewhere near 2.78 liters with rudimentary maths taking the volumes a % of the rb30 figures...

some people may be able to guess whaere im going with this?
 
1 - 20 of 25 Posts
Top